To provide cellular wireless communication service, a wireless service provider typically operates a radio access network (RAN) that defines coverage areas in which subscriber devices can be served by the RAN and can thereby obtain connectivity to broader networks such as the public switched telephone network (PSTN) and the Internet.
A typical RAN may include one or more base transceiver stations (BTSs) (e.g., macro network cell towers and/or femtocells), each of which may radiate to define one or more wireless coverage areas such as cells and cell sectors in which subscriber devices can operate. Further, the RAN may include one or more radio network controllers (RNCs) or the like, which may be integrated with or otherwise in communication with the BTSs, and which may include or be in communication with a switch or gateway that provides connectivity with one or more transport networks. Conveniently with this arrangement, a cell phone, personal digital assistant, wirelessly equipped computer, or other subscriber device that is positioned within coverage of the RAN can then communicate with a BTS and in turn, via the BTS, with other served devices or with other entities on the transport network.
In each coverage area, a RAN will typically broadcast a pilot signal that serves to notify subscriber devices of the presence of the coverage area. In practice, when a subscriber device enters into a coverage area and detects a pilot signal of a sufficient strength, the device may transmit a registration message to the RAN to notify the RAN that the device is in the coverage area, and the device may then operate in an “idle” mode in the coverage area. In the idle mode, the device is not actively engaged in a call or other traffic communication, but the device regularly monitors overhead signals in the coverage area to obtain system information and page messages for instance.
When a RAN seeks to connect a call or other communication to an idle subscriber device, the RAN may transmit a page message to the device in the coverage area where the device last registered. Upon detecting the page message, the device may then respond to the RAN. The RAN may then connect the communication to the device, thereby transitioning the device to an “active” state.
In general, wireless communications between a RAN and subscriber devices may occur on one or more carrier frequencies, also referred to as channels. A channel can take any of a variety of forms. By way of example, a channel can be defined as a specific frequency block, such as a 1.25 MHz block or a 5 MHz block in a profile frequency band used by the wireless service provider, such as 800 MHz (cellular band), 1.9 GHz (PCS band), or 2.5 GHz (BRS/EBS band). For instance, if a wireless service provider operates in the 800 MHz cellular band, coverage areas of the wireless service provider's RAN will typically operate with channels defined near 800 MHz. And if a wireless service provider operates in the 1.9 GHz band, coverage areas of the wireless service provider's RAN will typically operate with channels defined near 1.9 GHz. In practice, each channel may actually be defined as one frequency block for “forward link” communications from the RAN to subscriber devices and a corresponding but separate frequency block for “reverse link” communications from subscriber devices to the RAN.
On a given channel, communications between the RAN and subscriber devices may then further be carried on various sub-channels, also themselves referred to as channels. The forward-link, for instance, may define a pilot channel for carrying the pilot signal noted above and may further define a paging channel to carry page messages to subscriber devices, other overhead channels to carry system parameter information and the like, and a number of traffic channels to carry bearer traffic (e.g., call traffic) to subscriber devices. The reverse-link, on the other hand, may define an access channel to carry call-initiation messages and the like, and a number of traffic channels to carry bearer traffic to the RAN.
Each of these sub-channels may be defined in various ways, such as through code-division multiplexing or time-division multiplexing for instance. In a CDMA system, for example, communications in a given coverage area are typically spread spectrum modulated with a pseudo-noise offset (PN-offset) code associated with the coverage area, and various sub-channels such as the pilot channel, paging channel, and traffic channels are further spread spectrum modulated with a Walsh code specific to the sub-channel. In other systems, such as CDMA 1xEV-DO systems for instance, the various sub-channels may be defined through time-division multiplexing on the channel carrier frequency. Other examples are possible as well.
A coverage area that has a relatively low level of traffic, such as in a rural environment, may be engineered to operate with a single channel, such as a single 1.25 MHz frequency block (or pair of blocks) in the wireless service provider's profile frequency band. On the other hand, a coverage area that has a relatively high level of traffic, such as in an urban environment, may be engineered to operate with multiple channels, such as multiple 1.25 MHz frequency blocks (or pairs of blocks) in the wireless service provider's profile frequency band. Addition of channels to a coverage area serves to multiply coverage capacity in the coverage area.
When a subscriber device enters into a coverage are that provides service on multiple channels, an issue for the subscriber device is which channel the device should idle on. For instance, if a coverage area provides service on channels A, B, and C in a given coverage area, a subscriber device entering the coverage area my need to determine whether to idle on channel A, on channel B, or on channel C. Correspondingly, the RAN itself may also need to determine which channel the subscriber device will idle on, so that the RAN can direct any applicable page messages to the subscriber device on that channel.
To facilitate selection of a channel, a RAN may broadcast in each coverage area a “channel list message” (CLM) that lists the channels on which the RAN communicates in the coverage area, and a subscriber device may be arranged to receive the CLM and to apply a predefined channel-selection process to select a channel from among those listed in the CLM, and to then idle on the selected channel. Further, the RAN itself may also be arranged to apply the same channel-selection process so as to determine the channel on which the subscriber device will idle in the coverage area.
The predefined channel-selection process may be a hashing algorithm keyed to an identifier of the subscriber device, such as a device serial number or directory number, to help randomize distribution of subscriber devices among the available channels. By way of example, the hashing algorithm may operate on the subscriber identifier to produce an index value that points to a particular place in the CLM and therefore identifies which channel to use. For instance, given a CLM that lists channels A, B, and C, a hash result of 0 to 0.33 may point to channel A, a hash result of 0.34 to 0.66 may point to channel B, and a hash result of 0.67 to 1.0 may point to channel C. As a simplified example, such an index value could be produced by taking one tenth of the last digit of the device's serial number, or taking one hundredth of the last two digits of the device's serial number. However, the details of the hashing algorithm are not critical. Further, other channel-selection processes could be applied as well.
In example implementation, one of the channels in a multi-channel coverage area may be deemed a primary channel on which the RAN will broadcast the CLM and subscriber devices will receive the CLM. (Alternatively, the CLM may be broadcast on each channel in the coverage area.) Each subscriber device may be provisioned with logic, such as a preferred roaming list (PRL), that directs the subscriber device to the applicable primary channel when the subscriber device enters into such a coverage area. The subscriber device may then read the CLM broadcast on that channel and may apply the defined channel-selection process to select one of the channels on which to idle. The CLM in this implementation may list both the primary channel and one or more secondary channels on which the RAN communicates in the coverage area. Thus, through application of a hashing algorithm or other channel-selection process, a subscriber device entering the coverage area can select one of the available channels on which to communicate with the RAN.